Stores: Externally tracked state and reactive collections (#4483)

* map signals mutably

* boxed signals

* remove mutable borrow type from boxed writable

* improve map mut example

* restore boxed_mut helper

* make boxed readable/writable types copy

* Move away from the ReadOnlySignal alias in examples

* automatically convert Write

* Fix some tests

* ReadSignal and WriteSignal

* move read only signal alias

* make maps copy

* store prototype

* implement derive macro

* Handle generics in the derive macro

* Make Selector boxable

* derive boxed conversion

* Get rid of store type

* Remove hardcoded type from derive macro

* selector -> store

* Refactor store implementation

* more vec methods

* todo mvc store example

* Implement Storable for HashMap

* fix write

* restore sorting logic in todomvc

* derive readable and writable

* improve todomvc store example

* Result store

* Option store

* collect dead subscribers

* fix clippy and formatting

* recognize some common foreign types automatically

* fix foreign stores in props

* slice and array selectors

* clean up store example

* writable is child owned

* box selector

* read and write to builtins

* re-use the proc macro in the derive macro

* Switch to a extension trait based approach

* switch to extension traits in the derive macro

* transposed method

* derive enums

* Expose Store::new

* remove stores from the prelude

* More consistent naming scheme for SelectorScope methods

* document hashmap methods

* document index extension

* document option ext

* document result ext

* document slice extension

* document the vec extension

* make more methods borrow the store mutably

* Move to impls to have higher priority over the builtin write extension traits

* fix deadlock

* finish stores documentation

* Document the store macro

* cleanup docs and organization

* finish derive docs

* fix typo

* fix clippy

* fix doc tests

* fix derive macro with generics

* fix clippy

* test and fix empty structs

* clean up todomvc store example

* default to a boxed store writer to make it easier to type when providing to the context api

* fix cargo doc

* fix clippy in store example

* relax generational box lifetime bounds

* relax bounds

* relax signal bounds

* fix compilation

* read store

* relax bounds on default store impls

* fix enum derive

* Convert to readsignal and writesignal automatically

* simplify type matching logic

* add write store

* unsized stores

* shrink the path vec type

* use more concrete types

* remove opaque types

* remove copy bounds

* use lens as generic name everywhere

* more consistent borrow semantics

* use a concrete type for the signal metadata and mention references in the map docs

* improve todomvc store docs

* document store derive macro internals

* refactor macro

* improve selector node documentation

* fix clippy

* add btreemap

* fix doc tests

* more option methods

* fix doc

* fix clippy

* add a bunch more result methods

* add a bunch of bounds to the iterators

* fix clippy

* remove option from subscribers

* add store macro to generate extension traits

* fix store example

* fix deadlock

* fix docs

* fix doc tests

* fix clippy

* add stores to public api

* add store macro, and then update todomvc_store example

---------

Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/core/src/reactive_context.rs

@@ -335,6 +335,21 @@ impl Default for Subscribers {
 }
 
 impl Subscribers {
+    /// Create a new no-op list of subscribers.
+    pub fn new_noop() -> Self {
+        struct NoopSubscribers;
+        impl SubscriberList for NoopSubscribers {
+            fn add(&self, _subscriber: ReactiveContext) {}
+
+            fn remove(&self, _subscriber: &ReactiveContext) {}
+
+            fn visit(&self, _f: &mut dyn FnMut(&ReactiveContext)) {}
+        }
+        Subscribers {
+            inner: Arc::new(NoopSubscribers),
+        }
+    }
+
     /// Create a new list of subscribers.
     pub fn new() -> Self {
         Subscribers {